Forum Discussion

willald's avatar
willald
Explorer II
Jun 24, 2021

white dust coming out of AC vents - any ideas?

We noticed since the end of our last trip (early June), that when air conditioning is running, the vents seem to be spewing out this white dust, constantly.

After we got home and parked it, came out to the RV a few days later, and underneath one vent, there is a pretty large pile of this white dust, that had all come out of that one vent. Air conditioner had not been running, but still a bunch came out of that one vent. Cleaned it up, came back and checked it again today, and now there is yet *another* pile of the white dust, under just that one vent.

Filters were cleaned just before last trip, and still look pretty clean. Its pretty obvious this is coming from somewhere in the ducting, probably close to that one vent.

Since this pile keeps forming even when AC isn't running, starting to think critter infestation of some kind, but there is no other evidence whatsoever of critters being inside. How could they get up inside the vents, anyway? I did 'punch' the ceiling several places where ducts are, thinking if there was a critter, you'd hear stirring. Nothing. Looked down ducts as best I could, again, no evidence of any critters.

Its as if the foam insulation in there has suddenly started working loose and coming out in tiny pieces. Rig is 9 years old, this is first time this has happened.

Has anyone else experienced this, or might know what it is and how best to fix?
Class A
  • DrewE's avatar
    DrewE
    Explorer II
    Jun 24, 2021
    I'd remove the vent louvre from the ceiling and have a look inside with a flashlight and mirror (or a borescope, if you want to go the high tech route).
  • ScottG's avatar
    ScottG
    Nomad
    Jun 24, 2021
    Mine spewed out bits of Styrofoam even without the ac running. Just fell out going down the road.
    They use a large hole-saw to make the vent holes and it makes a mess. I removed each vent and used a mirror and shop vac to get it all out. There was a ton of it up there that collected in every little corner.
  • willald's avatar
    willald
    Explorer II
    Jun 24, 2021
    ScottG wrote:
    Mine spewed out bits of Styrofoam even without the ac running. Just fell out going down the road.
    They use a large hole-saw to make the vent holes and it makes a mess. I removed each vent and used a mirror and shop vac to get it all out. There was a ton of it up there that collected in every little corner.


    Good idea, the shop vac. Think I’ll get it out, and try that. Haven’t used the shop vac for a while, this is a good excuse to get it out and give it a workout.

    Will
  • ScottG's avatar
    ScottG
    Nomad
    Jun 25, 2021
    willald wrote:
    ScottG wrote:
    Mine spewed out bits of Styrofoam even without the ac running. Just fell out going down the road.
    They use a large hole-saw to make the vent holes and it makes a mess. I removed each vent and used a mirror and shop vac to get it all out. There was a ton of it up there that collected in every little corner.


    Good idea, the shop vac. Think I’ll get it out, and try that. Haven’t used the shop vac for a while, this is a good excuse to get it out and give it a workout.

    Will


    I had to stuff a length of heater hose into the vac's hose so it would fit up into the ducts.
    Good luck!
  • ItsyRV's avatar
    ItsyRV
    Explorer
    Jun 25, 2021
    One remote possibility that I doubt is the cause, but... Grab some of the dust and put it on white sheet of paper. Place another sheet over it and rub them together. Is the resulting smudge silverish? If so, your evap may be disintegrating. Have you recently cleaned the A/C or sprayed anything up into the return air duct? Your A/C is way too young for this to be a normal age issue, so if the aluminum is disintegrating, you need it checked quickly.
  • willald's avatar
    willald
    Explorer II
    Jun 25, 2021
    ItsyRV wrote:
    One remote possibility that I doubt is the cause, but... Grab some of the dust and put it on white sheet of paper. Place another sheet over it and rub them together. Is the resulting smudge silverish? If so, your evap may be disintegrating. Have you recently cleaned the A/C or sprayed anything up into the return air duct? Your A/C is way too young for this to be a normal age issue, so if the aluminum is disintegrating, you need it checked quickly.


    Interesting thought, but if that was the case, why is the white dust mostly piling up, when the air conditioner isn’t even running?

    I do plan this weekend, to get up on the roof, take the cover off of the air conditioner and have a look around for any clues as to what’s going on. Want to make sure the ducting hasn’t somehow been compromised in there, to the point it’s allowed a critter of some kind to get in.

    Will
  • DrewE's avatar
    DrewE
    Explorer II
    Jun 25, 2021
    The part of the air conditioner on the roof is (or at least should be) separated from the ductwork side by a solid barrier, of course with some wires and tubes going through it. Outside air and inside air do not mix by design. If you think the source might be the air conditioner itself, it would be better to remove the inside cover/louver on the air conditioner unit and examine things from the inside. (There's no ducting as such on the outside side part of the air conditioner, just the shroud over the condenser, its fan, and the other external bits.)

    Unless the powder is appearing from that air conditioner unit itself, I'd tend to suspect a source near where the pile is forming instead; but there's certainly no problem with taking a look at everything. If nothing else, it's well worth looking at the outside part of the air conditioner and cleaning out dirt or debris if needed to keep it working efficiently and effectively.
  • dougrainer's avatar
    dougrainer
    Nomad
    Jun 25, 2021
    DrewE wrote:
    The part of the air conditioner on the roof is (or at least should be) separated from the ductwork side by a solid barrier, of course with some wires and tubes going through it. Outside air and inside air do not mix by design. If you think the source might be the air conditioner itself, it would be better to remove the inside cover/louver on the air conditioner unit and examine things from the inside. (There's no ducting as such on the outside side part of the air conditioner, just the shroud over the condenser, its fan, and the other external bits.)

    Unless the powder is appearing from that air conditioner unit itself, I'd tend to suspect a source near where the pile is forming instead; but there's certainly no problem with taking a look at everything. If nothing else, it's well worth looking at the outside part of the air conditioner and cleaning out dirt or debris if needed to keep it working efficiently and effectively.


    Bingo. There is NOTHING in a RV rooftop AC unit that will produce debris or dust. What DOES produce this dust is, at EACH roof AC you need to make sure there is NO possible way the cavity of the roof between to top and the interior ceiling has open egress areas. If so, the AC unit will "pull" air and debris from this cavity as long as from the inside of the RV. The cavity will be behind the AC filter's, hence the fine debris. This is where AC Foil Tape comes in very handy to seal off those areas. If your AC units have the inside Plenum mount, you remove this mount and you will see the gaps on the 14 inch square roof cut out. SEAL those gaps and your problem goes away. IF top mounted AC you will have to remove the unit from the roof and do the same thing. Doug

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